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Chapter 2. How Camera Raw Works > Bit Depth, Dynamic Range, and Color

Bit Depth, Dynamic Range, and Color

We use numbers to represent a pixel's tonal value—how light or dark it is—and its color—red, green, blue, yellow, or any of the myriad gradations of the various rainbow hues we can see.

Bit Depth

In a grayscale image, each pixel is represented by some number of bits. Photoshop's 8-bit/channel mode uses 8 bits to represent each pixel, and its 16-bit/channel mode uses 16 bits to represent each pixel. An 8-bit pixel can have any one of 256 possible tonal values, from 0 (black) to 255 (white), or any of the 254 intermediate shades of gray. A 16-bit pixel can have any one of 32,769 possible tonal values, from 0 (black) to 32,768 (white), or any of the 32,767 intermediate shades of gray. If you're wondering why 16 bits in Photoshop gives you 32,769 shades instead of 65,536, see the sidebar “High-Bit Photoshop,” later in this chapter (if you don't care, skip it). So while pixel dimensions describe the two-dimensional height and width of the image, the bits that describe the pixels produce a third dimension that describes how light or dark each pixel is—hence the term bit depth.


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